MINSK/MOSCOW: Belarusians chanting "Step down!" filled the centre of the capital Minsk on Sunday in the biggest protest so far against what they said was the fraudulent re-election a week ago of longtime president Alexander Lukashenko.

Russia said it would offer Lukashenko military help if necessary, but there was no visible police presence at the protest, which attracted around 200,000 people, a Reuters reporter estimated. At least two protesters have died and thousands have been detained in a crackdown since the vote.

The atmosphere was celebratory, with people carrying the red and white flags used in Belarus after the 1991 breakup of the Soviet Union before Lukashenko restored the Soviet version four years later.

"We all want Lukashenko to step down," said a 31-year-old worker who gave his name as Alexei. "For now we are asking, but we will get sick of asking."

Opponents of Lukashenko, in power for 26 years, say the vote was rigged to disguise the fact that he has lost public support. He denies losing, citing official results that gave him just over 80% of the vote.

The Kremlin said Russian President Vladimir Putin had told Lukashenko Moscow was ready to assist Belarus in accordance with a collective military pact if necessary and that external pressure was being applied to the country.

It did not say where from.

Shortly before the opposition protest, there was tight security as Lukashenko's supporters gathered in central Minsk for the first time since the election to watch him give a fiery speech.

Lukashenko, who has alleged a foreign-backed plot to topple him, said NATO tanks and planes had been deployed 15 minutes from the Belarusian border.

"NATO troops are at our gates. Lithuania, Latvia, Poland and our native Ukraine are ordering us to hold new elections," he said, adding that Belarus would "die as a state" if new polls were held. "I have never betrayed you and will never do so."

NATO said it was closely monitoring the situation in Belarus, but that there was no military build-up at the country's western border.

The Belarusian army would hold drills in the west of the country from Aug. 17-20, Russia's RIA news agency reported.

'JOIN US'

Sviatlana Tsikhanouskaya, Lukashenko's opposition rival in the contested election, fled to neighbouring Lithuania on Tuesday. She had called for the huge "March of Freedom" through Minsk and in other towns and cities on Sunday in support of an election recount and is forming a national council to facilitate a power transfer.

Maria Kolesnikova, an opposition politician who has allied with Tsikhanouskaya, referred to Lukashenko as "the former president", said he should quit, and appealed to state officials to abandon him.